With a few exceptions, tradition and technology have favored transillumination pulse oximetry in the operating theater. The principle of operation of the pulse oximeter is fairly simple but is arguably the most important development in anesthesia monitoring in the twentieth century. Two wavelengths of light (usually 660 nm and 940 nm) are used to spectrophotometrically determine the ratio of oxidized to reduced hemoglobin noninvasively as well as to determine the pulsatility of blood plethysmographically. Presently, the most common application of this in the operating theater is via transillumination through the capillary bed of a peripheral digit. However, it is not unusual for multitrauma and thermally injured patients to either have severe peripheral vasoconstriction or to have severely damaged (or missing due to amputation) peripheral vascular beds. Reflectance oximetry rather than transillumination oximetry was the earliest investigative form of the technique. Transillumination pulse oximetry, without question, is the most effective form when oximetry is obtained through skin. However, when skin is not interposed as a barrier to capillary bed access, reflectance pulse oximetry easily can be achieved with very accurate results. The effect is achieved by the backscattering of incident bispectral light that traverses and, on reflection from nonabsorptive collagenous tissues, retraverses formed elements in the blood back to the oximetric detector. Rather than superseding transillumination pulse oximetry, this technique broadens the scope of possible monitoring sites, adding to the clinician's armamentarium.
Previously, three devices were needed to accomplish the functions provided by this invention. An oropharyngeal airway and a bite block are sold as two separate pieces that are used at different times and in different situations. A pulse oximeter sensor is used to take readings for the determination and measurement of oxygen saturation in the blood without taking a blood sample. Prior art devices have combined the oropharyngeal airway with the capability to perform transilluminance pulse oximetry through the posterior tongue or have placed oximeter sensors farther down the trachea then is proposed by this invention.
The oropharyngeal airway is used during surgical anesthesia. If the oropharyngeal airway is inserted prior to induction of anesthesia or left inserted upon emergence from anesthesia, then there is the possibility that the patient could be stimulated to vomit and aspirate stomach contents resulting in an often fatal event for the patient. Also, the oropharyngeal airway will cause uncomfortable stimulations deep in the throat and thus cause gagging and the impingement of the teeth upon the endotracheal tube prior to extubation if the patient awakens from anesthesia. Thus the oropharyngeal airway may not be inserted until the patient is profoundly sedated and must be removed once the patient begins to awaken. The oropharyngeal airway establishes a ventilatable airway in a patient who is unconscious.
The bite block maintains an oral aperture for suction and the passage of air or vomit. The bite block is also used to prevent biting of an endotracheal tube. The bite block does not stimulate the posterior tongue or pharynx.
Prior pulse oximeter sensors inserted through the mouth are usable only when the patient is under general anesthesia. These pulse oximeter sensors are inserted to reach the larynx area, for example, U.S. Pat. No. 5,282,464 to Brain et al. Another known method uses transillumination pulse oximetry of the posterior tongue, but this method may not be used with a patient, who is awake, for example, U.S. Pat. No. 5,205,281 to Buchanan. Also, the posterior tongue is not the most accessible body part to take oximetric measurements.
Conventional pulse oximetry in the severely burned patient can be a significant challenge, yet this monitoring data is vital in operating room and intensive care settings. Most current oximetric approaches depend upon available peripheral sites permitting transillumination oximetry and indeed, this method is sufficient for most surgical conditions and procedures. Unfortunately, patients with severe burns often have few sites for the effective placement of the transilluminating pulse oximeter sensor. In addition, these patients often have severe circulatory compromise rendering the peripheral pulse oximeter less efficient.
Recent studies indicate that oral pulse oximetry is a superior modality when compared to peripheral transillumination pulse oximetry. A variety of studies have shown that oral pulse oximeters are more reliably and rapidly responsive than peripheral pulse oximeters. However, these studies use oral transillumination pulse oximetry, held in place via complex devices or pieces of improvised malleable metal. Oral secretions, equipment failure, and placement difficulty often render these techniques ineffective.
Reflectance oximetry can be a useful tool where a capillary bed is easily accessible. Indeed, it is used commonly and effectively among intrapartum and neonatal patients whose capillary beds are easily accessed through their skin. The technique has also been applied to adult and pediatric burn patients by placing the reflectance sensor in wounds or over hyperemic sites such as healed partial thickness bums.
There are other often overlooked capillary beds readily accessible in most adult bum patients that are as amenable to reflectance oximetry as the forehead of the premature infant. The buccal surface, posterior soft palate, hard palate and proximal posterior pharynx of a burned patient are seldom compromised no matter how severe the burn, and the capillary beds are very close to the surface in those areas. Transillumination pulse oximetry of the tongue and cheek has been documented as a viable method of monitoring, but not everyone has the equipment available to place a transilluminating pulse oximeter on the tongue or cheek. A reflectance pulse oximeter has the bispectral emitter and the sensor in a side-by-side configuration rather than in opposition. The device may be placed flat upon a suitable capillary bed and it thus becomes a reflectance pulse oximeter. In this manner, a standard disposable finger pulse oximeter probe may simply be placed flat against the buccal surface, thus rendering it a reflectance rather than a transilluminating device.
Notwithstanding the usefulness of the above-described devices, and the above-identified recognized viability of transilluminating buccal pulse oximetry, a need exists for a more convenient device that combines a bite block with an oropharyngeal airway. Additional convenience is obtained by including a pulse oximeter sensor with a device that includes the bite block and the oropharyngeal airway.